The physical and aesthetic requirements for a particular piece of leather are highly dependent on the designated end use for the leather. For example, in one application, a piece of leather may be treated primarily to provide it with strength; its other aesthetic qualities being of much less importance for its intended application. In upholstery applications, both softness and strength are required. In vehicle upholstery, as for example in automobiles and aircraft, the treated leather should also not contribute to fogging.
Treating hides and skins to form leather involves a number of interdependent chemical and mechanical operations. Each of these operations has an effect on the final properties of the treated leather product. See Leather Facts, New England Tanners (1972). One important chemical operation in the treatment of leather is fat-liquoring. Fatliquoring is used to impart the desired strength and temper properties to tanned leather. Fatliquors lubricate the leather fibers so that after the leather is dried its fibers are capable of sliding over one another. In addition to regulating the pliability of the leather, fatliquoring contributes greatly to the tensile and tearing strength of the leather. Fatliquoring also affects the tightness of the break or crease pattern formed when the grain surface is bent inward; the object being to produce a leather which leaves no or few fine wrinkles when bent. The subject matter of applicants related copending patent application identified above was to selected amphiphilic copolymers which performed both as retanning and fatliquoring agents and provided the treated leather with a number of desirable properties including, in its preferred embodiment, improved water resistance.
The basic ingredients used in conventional fatliquoring operations are water insoluble oils and fatty substances such as raw oils and sulfated and sulfited oils. Typically the weight percent of fatliquor oil on weight of leather ranges from 3 to 10 percent. The manner in which the oil is distributed throughout the leather affects the character of the leather and subsequent finishing operations. In order to obtain a uniform oil coating over a large surface of leather fibers it is typically necessary to dilute the oil with an organic solvent or preferably to disperse the oil in an aqueous system using emulsifiers. See Leather Technician's Handbook, J. H. Sharphouse, Leather Producers' Association (1971) chapters 21 and 24. The basic ingredients used in fatliquoring leather have been found, however, to have a significant adverse impact on the ultimate fogging characteristics of the leather.
"Fogging" as used herein means the condensation of evaporated volatile substances, which come from the interior outfit of a vehicle, on glass windows, particularly on the windshield (See DIN 75201 (April 1988)). Fogging is undesirable because it hinders the unimpeded vision of the driver, especially during darkness, and particularly when the driver is faced with lights of oncoming traffic. A secondary effect is caused by dust and dirt particles brought into the interior through the fan; these becoming bound to the glass surface causing further visibility impairment.
Das Leder, 1988, Issue 9, Fat Liquors and "Fogging"--the Influence of Various Raw Materials and their Processing Methods, M. Kaussen, pages 161-165 (translation) states that fogging results from all volatile substances in the interior equipment including from fabrics, plastics and leather. Analyses of fogging derived from leather show that a number of the chemicals used in conventional leather treatment operations contribute to fog such as for example, residual natural fats in wet blues; phenolic fungicides; dyestuffs; phthalates and mineral oil additives used as anti-dust agents; and solvents, emulgators (sic-emulsifiers) and plasticizers used in finishes. However, the most important of all the factors contributing to fogging due to leather has been found to be the fats, both natural fats and fatliquors, such as triglycerides and free fatty acids, which directly result from the fatliquoring leather treatment step. This publication stresses the importance of a degreasing step to reduce leather fogging and generally suggests that fatliquors used in car upholstery leather manufacture should, if possible, contain no solvents or preferably be substances which are not very volatile. The publication concludes, based on reflexion (sic-reflectance) fogging measurements, that fatliquors based on paraffin sulphonates, chloroparaffin sulphonates", wool fat sulphitates (sic-sulphites) and fish oil sulphitates"' (sic-sulphites) show good fogging results. Fogging Characteristics of FatLiquors and CarSeat Leathers: Part 1: Preliminary Studies, Samir Das Gupta (May 11, 1989), discusses the state of the art in leather fogging testing, particularly reflectance tests and gravimetric tests. In evaluating these tests a number of conventional fatliquors were used. Attempts at correlating the extent of volatiles in the fatliquor and the fogging results obtained were not successful. In some respects, the conclusions reached in this evaluation, particularly with respect to sulphonated fish oil and sulphonated chloroparaffins, were exactly the opposite of the Das Leder study reported above. One reason for this was reported to be due to significant differences between the reflectance fogging tests and gravimetric tests; the gravimetric test being considered a more rigorous test.
Some automakers have published their own fogging test procedures and have established their own fogging requirements. Some of these are reflectance tests, as for example Ford Motor Company, and some also incorporate gravimetric tests, such as Daimler-Benz.
It is an object of the present invention to provide a polymer for retanning and fatliquoring leather which provides the treated leather with both the requisite strength and temper characteristics typically associated with conventional fatliquors and significantly reducing fogging.
It is a further object of the present invention to provide a retanning fatliquoring polymer which meets gravimetric fogging requirements.